Modern yachts have fore and aft sails, including a mainsail supported by a mast. The mainsail, which is triangular, is hitched at its bottom edge, or foot, to a boom that can swing about the lower part of the mast in either direction in relation to the longitudinal axis of the boat. The mainsail is raised or lowered by hoisting a halyard coupled to the upper corner, or head, of the mainsail. Raising the halyard causes the sail to extend such that the sail's forward edge, or luff, runs parallel to the mast.
Various track and slide assemblies have been used to guide the sail along the mast, making it easier to raise and lower the sail. These assemblies also link the aft edge of the mast to the sail luff. Typical assemblies include low-friction sail slides, attached to the luff at regular intervals, that fit onto a rail or into a track that extends along the longitudinal axis of the mast.
Prior art track and slide assemblies use tracks or rails that extend along the mast from the boom to the top of the mast. Some tracks and rails are attached to the mast, whereas others are integrally formed with the mast itself. Both integral and non-integral tracks and rails stiffen the mast. In addition, both integral and non-integral tracks and rails are difficult to maintain: if a sail slide becomes irretrievably jammed in the track, the entire track (or mast, for integral tracks) must be removed. Alternatively, the crew must go aloft to fix the problem in place. Both options are time-consuming for yachts with taller masts, and going aloft can be dangerous and impractical, depending on the conditions.
Conventional sail slides, which run in a channel or groove in a mast track, are attached to the mainsail with shackles or are sewn in position. Unfortunately, friction between the slides and the track causes the slides to lock in place, preventing the sail from being raised or lowered. For example, twisting or torquing forces by the mainsail exerted on rectangular slides bind the slides to the track, preventing sliding movement and making it impossible to control the mainsail. Pulling forces exerted on the slides by the mainsail may pull the slides from the track, depending on the design of the groove.
Ball track slides, which use plastic balls and a rail mounted on the mast to absorb loads except those in the direction of movement, do not suffer from friction locking. High loads flatten the balls, however, degrading the balls' bearing-like action. Ball track slide assemblies also weigh more than conventional assemblies and are more susceptible to jams due to corrosion and dirt. In addition, the rails for ball track slides tend to be much heavier than the tracks for conventional sail slides.
The linkage between the slides and the sail luff also affects the utility of the track and slide assembly. If the slides are rigidly coupled to reinforcements, or battens, attached to the luff of the sail, then wind pushing on the battens may cause the battens to push, in turn, on the slides, disrupting the link between the slides and the sail. These forces may also detach the slides from the track.